There has been much debate about the audio recordings of 911 calls on the night George Zimmerman shot Trayvon Martin — were the cries for help heard in the background from Martin or from Zimmerman? Those who believe Zimmerman's claim of self-defense said he was the one calling for help — suggesting Martin had the upper hand in the fight — while others have insisted it was Martin begging for his life.

Now, two forensic experts have weighed in: it is their belief that the screams are not George Zimmerman's, but they cannot say conclusively that they're Trayvon Martin's.

Using sophisticated voice match software, Tom Owen, forensic consultant for Owen Forensic Services LLC and chair emeritus for the American Board of Recorded Evidence, told the Sentinel that there was only a 48% chance that it was Zimmerman crying for help on the tape.

Based on that result — and the fact that one would need at least a 90 percent match to confirm a positive — Owen says that the voice is not Zimmerman's "with reasonable scientific certainty."

Without using any software, audio engineer and forensics expert Ed Primeau reached a similar conclusion.

Primeau didn't use Owen's CSI-style voice analysis software, but instead relied on audio enhancement and his own well-trained ear to compare the screams to Zimmerman's voice on a 911 call he made shortly before the killing.

"That's a young man screaming," Primeau said.

Primeau is confident that the voice heard on the 911 tapes is indeed Trayvon Martin's. Owen was unable to confirm that, because he didn't have a sample of Martin's voice to compare it to.

While it's unclear if these experts would be called as witnesses in a trial — if Zimmerman is actually arrested — their unofficial testimony is further contradiction of Zimmerman's version of events.